Strip line to waveguide transition

ABSTRACT

Apparatus is disclosed for coupling a wave transmitted between a waveguide and a strip line. In particular, the strip line is composed of a conductor, a dielectric substrate and an earth (or ground) conductor. In accordance with teachings of this invention the coupling is achieved by inserting a slot mode between the strip propagation mode and the waveguide mode in a strip line to waveguide transition. More specifically, a slot is formed in the earth conductor of the strip line and the slot is disposed to intersect or to traverse the strip line conductor to achieve the desired coupling.

iliiited States Patent 1191 Ito et al.

1 1 May 8, 1973 [541 STRIP LINE T0 WAVEGUIDE TRANSITION [21] Appl. N0.: 208,609

[30] Foreign Application Priority Data Dec. 23, 1970 Japan ..45 117120 52 US. Cl. ..333/21 R, 333/27, 333/84 R, 333/84 M 51 Int. Cl. ..H0lp 1/16, HOlp 3/08, HOlp 5/08 [58] Field of Search ..333/84, 84 M, 11, 333/21, 21 A [5 6] References Cited UNITED STATES PATENTS 3,462,713 8/1969 Knerr 333/84 X 3,654,572 4/1972 Napoli ..333/21 R 3,577,181 5/1971 Belohoubek... I. 3,579,149 5/1971 Ramsey OTHER PUBLICATIONS Cohn-"Slotline on a Dielectric Substrate in IEEE Transactions on Microwave Theory and Techniques Vol. MTT 17 No. 10 Oct. 1969; pp. 768-770.

Primary Examiner-Rudolph V Rolinec Assistant Examiner-Marvin Nussbaum Attorney-Hans, Sears, Staas, Halsey & Santorelli [57] ABSTRACT Apparatus is disclosed for coupling a wave transmitted between a waveguide and a strip line. In particular, the strip line is composed of a conductor, a dielectric substrate and an earth (or ground) conductor. In accordance with teachings of this invention the coupling is achieved by inserting a slot mode between the strip propagation mode and the waveguide mode in a strip line to waveguide transition. More specifically, a slot is formed in the earth conductor of the strip line and the slot is disposed to intersect or to traverse the strip line conductor to achieve the desired coupling.

10 Claims, 13 Drawing Figures PATENTED W 81915 SHEET 1 [IF 2 FlG.l PRIOR ART FlG.-2 PRIOR ART FIG.

Flea PRIOR ART FIG.6

FIG.7

STRIP LINE T WAVEGUIDE TRANSITION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to transducers or coupling apparatus, and in particular to a strip line to waveguide transition, adapted for coupling the wave transmitted through a strip line to a waveguide.

2. Description of the Prior Art Many types of strip line to waveguide transitions have been proposed for coupling wave energy between a strip line and a waveguide. With regard to the drawings, FIGS. 1, 2 and 3 show various strip line to waveguide transitions as suggested by the prior art. In FIG. 1, a transition is shown including a conductor 2 inserted into a waveguide 1 within its E plane; more specifically, the conductor 2 is mounted upon a dielectric substrate 3 and is disposed a distance lfrom a short circuit wall of the waveguide I, wherein Z is substantially equal to )t /4, where A, is the wavelength in the waveguide transmitted within the waveguide l. The device described with regard to FIG. 1 may be simply assembled and constructed; however, its transmission characteristics are not wideband.

In FIG. 2, a further transition of the prior art is shown as including a waveguide 11 and a metallic plate or finger 14 extending from a wall thereof. A strip line is disposed within the waveguide 11 and includes a conductor having an end portion connected to the metallic plate 14. Further, the strip line is connected to an inner wall of the waveguide 11. A device, such as described with regard to FIG. 2, has the defect of loss due to electrical and mechanical instability of connection.

In FIG. 3, there is shown an impedance transformation to a strip line 23, which is carried out by a metallic plate 25 inserted within a waveguide 21. The strip line 23 includes a conductor 22 which is connected to the metallic plate 25. Such a waveguide transducer may leak to the housing of the strip line, and spurious-mode resonance loss caused by radiation-mode is increased to the extent that the device shown in FIG. 3 is not applicable to multiplex radio communication apparatus.

SUMMARY OF THE INVENTION It is an object of this invention to couple wave energy between a waveguide and a strip line with a minimum loss of wave energy while achieving a broad bandwidth capability.

In accordance with this and other objects of this invention, the teachings of this invention are accomplished by forming a transition between a strip line and a waveguide by interposing a slot mode therebetween. More specifically, the strip line includes a conductor, a dielectric substrate and an earth conductor having a slot formed therein so as to intersect the strip line conductor. The strip line is disposed within the waveguide so that its electromagnetic field distribution is substantially aligned with that of the waveguide to effect the desired coupling.

BRIEF DESCRIPTION OF THE DRAWINGS:

In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings in which:

FIGS. 1, 2 and 3 show strip line-waveguide transitions of the prior art;

FIG. 4 is a perspective view of the slot mode in accordance with the teachings of this invention;

FIG. 5 is a partial perspective view of the relationship between a strip line and a slot mode in accordance with teachings of this invention;

FIG. 6 is a partially broken away, perspective view of a further embodiment of this invention;

FIG. 7 is a partially broken away, perspective view of another embodiment of this invention;

FIGS. 8 to 11 are partially broken away, perspective views of further embodiments of the strip line to rectangular waveguide transition in accordance with teachings of this invention; and

FIGS. 12 and 13 are partially broken away, perspective views of strip line to circular waveguide transitions in accordance with teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With regard to the drawings and in particular to FIG. 6, there is shown a strip line to waveguide transition comprising a strip line including a conductor 32 mounted upon a support member or plate 33, made of a suitable dielectric material such as ceramic or glass. As shown in FIG. 6, this strip line is inserted into a waveguide 31 having in one illustrative embodiment a rectangular configuration. More specifically, the strip line is so disposed within the rectangular waveguide 31 that the direction of the electric field indicated by an arrow identified by the letter E is disposed substantially parallel to the plane of the dielectric plate 33. Further, the strip line includes an earth (or ground) conductor 36, which is suitably mounted upon a metallic block 38, disposed in the waveguide 31 for providing a suitable means for mounting the strip line in a fixed relationship with the waveguide 31. As indicated in FIG. 6, the dielectric plate 33 is disposed between the earth conductor 36 and the conductor 32. In accordance with the teachings, of this invention, an elongated slot 37 of appropriate width is formed within the earth conductor 36 to traverse or intersect orthogonally an end portion or part 32' of the conductor 32. As indicated in FIG. 6, the conductor 32 resembles a question mark so that its curved or end portion 32 is disposed orthogonally to the slot 37.

The significance of the slot disposed within the earth conductor 32 of the strip line will be explained with regard to FIGS. 4 and 5. The distribution of the electromagnetic field formed by the slot 47 disposed within the earth conductor 46 is shown by the E and H planes in FIG. 4. It is significant that the electromagnetic field formed by the slot 47 is similar to the distribution of an electromagnetic field in a waveguide; as a result, the transformation from the waveguide mode to the slot mode is easily carried out over a wide bandwidth in accordance with the teachings of this invention. In FIG. 5, the strip line includes a conductor 42 with an end portion 42', a dielectric plate 43 and earth conductor 46 with a slot 47 formed therein so as to intersect orthogonally the end portion 42'. By so disposing the slot 47 orthogonally with respect to conductor 42, the transformation from the slot mode to the strip line mode can be accomplished over a wide bandwidth.

As shown in FIG. 6, the metallic block 38 used for mounting the strip line interrupts the propagation of the basic mode of the waveguide, because the length of the waveguide 31 is substantially decreased by the insertion of the block 38 at the side of the strip line. In a transition shown in FIG. 6, the open end of the slot 37 is disposed adjacent to the end portion 32 and unnecessary magnetic coupling may occur in that part 32 and the characteristics of the resultant transition may suffer. Though the effect of this unnecessary magnetic coupling can be decreased by configuring the part 32 of the conductor 32 to displace the conductor 32 from the open end of the slot 37, such displacement makes the conductor 32 longer and hence the loss of the conductor 32 is increased.

With regard to FIG. 7, another embodiment of this invention is shown as including a strip line formed by a dielectric plate 53, disposed between a conductor 52 and an earth conductor 56. A slot 57 is formed within the earth conductor 56, to have a continuous, proper curve bent toward a wall of a waveguide 51. Further, the conductor 52 has an end portion 52 disposed at an angle to the remaining portion of the conductor 52, to intersect orthogonally with the slot 57. As shown in FIG. 7, the dielectric plate 53 is cut at an angle with respect to a wall of a waveguide 51, to present an end surface 53, that is adjacent to and disposed along the bent portion or part 52 of the conductor 52. In such an embodiment, the magnetic coupling between the end of the slot 57 and the conductor 52 can be substantially neglected. More specifically, the end surface 53 is disposed substantially parallel to the end portion 52' and adjacent thereto; as a result, the disturbance within the electromagnetic field is decreased to a minimum. As the connection between the slot 57 and the end portion 52 is strengthened, the frequency characteristics of the transducer are improved, and wideband transformation can be obtained thereby. As shown in FIG. 7, the slot 57 is bent or curved toward a wall of the waveguide 51 in a manner similar to that described above. Hence, the conductor 52 may be shorter than that conductor shown in the embodiment of FIG. 6. Thus, the conductor loss is decreased and a small size, low loss strip line to waveguide transition is provided.

With regard to FIG. 8, there is shown a further embodiment of this invention in which a strip line is disposed within a waveguide 61 and includes a dielectric plate 63 disposed between a conductor 62 and an earth conductor 66. The earth conductor 66 is made of a suitable metallic material and has an appropriate thickness; a slot 67 is formed within the earth conductor 66 to separate the earth conductor 66 into two parts, one of which (the lower part as shown in FIG. 8) is extended with respect to the other.

In FIG. 9, a further improvement may be obtained from the transducer shown in FIG. 8, by disposing a tapered slot 77 within the ground conductor '76. More specifically, the slot 77 increases in width toward its open end to provide two tapered surfaces as shown in FIG. 9.

FIG. shows a further embodiment of this invention wherein impedance matching between the waveguide mode and the slot mode are obtained and wideband characteristics are improved. In particular,

the embodiment shown in FIG. 10 is similar to that shown in F IG. 6 with the exception that a block 89 is inserted within the waveguide 81 and has a dimension along a direction across the width of the waveguide, smaller than that of the metallic block 88.

In FIG. 11, there is shown a still further embodiment of this invention, in which the separate metallic blocks 88 and 89 of the embodiment of FIG. 10 are replaced by a single block 100. More specifically, the end surface of the block shown in FIG. 11 is tapered to provide a curved surface: As a result, the spacing between the tapered surface of the block 100 and the earth conductor 97 will be gradually increased.

The embodiments of this invention previously shown and discussed have each related to a waveguide of rectangular configuration. However, it is apparent as shown in FIGS. 12 and 13 that this invention is also applicable to waveguides of a circuit configuration. In FIG. 12, a strip line is disposed into a circular waveguide 121,, to be substantially paralleled with the E field as indicated by the arrow of the TE mode of the circular waveguide 121 The strip line includes an earth conductor 126 securely fixed to a metallic block 128,,. Further, the earth conductor 126 has a slot 127 disposed therein, dividing the earth conductor 126 into two parts. The upper part as shown in FIG. 12 is extended with respect to the lower part.

The transition shown in FIG. 13 is similar to the embodiment of FIG. 12, but has improved characteristics in that the earth conductor 136 has formed therein a slot 137 with surfaces that taper toward its open end.

The transitions described above are adapted for an unbalanced strip line, but it should be understood that these embodiments may also be used for a balanced strip line. The output and input outlets of the microwave circuits, and in particular millimeter wave circuits, are usually formed by waveguides. The circuit elements of such circuits are typically integrated on a strip line so that the transducer of this invention may be used for connecting the strip line to the output and input elements thereof. As a result of the use of this invention, a wideband and low loss radio equipment may be obtained.

As described above, in the strip line to waveguide transition of this invention, the waveguide mode is transduced to the slot mode whose distribution is similar to that of the waveguide mode. In turn, the slot mode is transformed to the strip propagation mode and as a result, impedance matching can be easily accomplished over a wideband. Further, because the slot is formed in the earth conductor of the strip line (or in the metallic carrier plate on which the strip line circuits are mounted), the structure of this transition is inherently simple. In the transforming from the slot mode to the strip propagation mode, the coupling between both modes can be controlled by the angle of intersection between the slot and the conductor, and wideband characteristics are obtained.

The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be efi'ected within the scope of the invention.

We claim:

l. A strip line to waveguide transition comprising:

a. a hollow waveguide for propagating electromagnetic waves in a waveguide mode along the axis of said waveguide;

b. a strip line for propagating electromagnetic waves in a strip line mode therealong and comprising a first conductive element, a second earth, conductive plate and a dielectric substrate disposed therebetween; and

c. a slot line for coupling the electromagnetic waves between said waveguide and said strip line, said slot line being formed within said conductive plate of said strip line substantially parallel to said axis of said waveguide, said conductive plate being disposed substantially parallel to the direction of the electric field of said electromagnetic waves propagated by said waveguide whereby the electric and magnetic fields of the electromagnetic wave propagated by said waveguide are aligned with the electric and magnetic fields of the electromagnetic wave propagated by said slot line, said first conductive element of said strip line disposed substantially orthogonal to said slot line whereby the electric and magnetic fields of the electromagnetic waves propagated by said strip line are smoothly coupled with said slot line.

2. Apparatus as claimed in claim 1, wherein said slot comprises at least one edge surface, said edge surface being configured in a curve directed toward a wall of said waveguide.

3. Apparatus as claimed in claim 1, wherein said slot forms first and second portions of said earth conductor, said first portion extending a greater distance along said waveguide than said second portion.

4. Apparatus as claimed in claim 1, wherein said dielectric member has an end surface disposed at an acute angle with respect to a wall of said waveguide, said first conductor having an end portion aligned in a substantially parallel relationship with said end surface.

5. Apparatus as claimed in claim 1, wherein said strip line has an end portion shaped as a question mark to orthogonally traverse said slot line.

6. Apparatus as claimed in claim 1, wherein said conductive plate has an edge portion and said slot line is formed within said conductive plate of said strip line, having opposed surfaces curved away from each other as said surfaces approach said edge portion.

7. Apparatus as claimed in claim 1, wherein said waveguide has a cross-section of a circular configuration.

8. Apparatus as claimed in claim 1, wherein said waveguide has a cross-section of a rectangular configuration.

9. Apparatus as claimed in claim 1, wherein a conductive member is disposed between the periphery of said waveguide and said conductive plate for supporting said strip line within said waveguide.

10. Apparatus as claimed in claim 9, wherein said support member includes a portion of reduced width disposed upon the periphery of said waveguide. 

1. A strip line to waveguide transition comprising: a. a hollow waveguide for propagating electromagnetic waves in a waveguide mode along the axis of said waveguide; b. a strip line for propagating electromagnetic waves in a strip line mode therealong and comprising a first conductive element, a second earth, conductive plate and a dielectric substrate disposed therebetween; and c. a slot line for coupling the electromagnetic waves between said waveguide and said strip line, said slot line being formed within said conductive plate of said strip line substantially parallel to said axis of said waveguide, said conductive plate being disposed substantially parallel to the direction of the electric field of said electromagnetic waves propagated by said waveguide whereby the electric and magnetic fields of the electromagnetic wave propagated by said waveguide are aligned with the electric and magnetic fields of the electromagnetic wave propagated by said slot line, said first conductive element of said strip line disposed substantially orthogonal to said slot line whereby the electric and magnetic fields of the electromagnetic waves propagated by said strip line are smoothly coupled with said slot line.
 2. Apparatus as claimed in claim 1, wherein said slot comprises at least one edge surface, said edge surface being configured in a curve directed toward a wall of said waveguide.
 3. Apparatus as claimed in claim 1, wherein said slot forms first and second portions of said earth conductor, said first portion extending a greater distance along said waveguide than said second portion.
 4. Apparatus as claimed in claim 1, wherein said dielectric member has an end surface disposed at an acute angle with respect to a wall of said waveguide, said first conductor having an end portion aligned in a substantially parallel relationship with said end surface.
 5. Apparatus as claimed in claim 1, wherein said strip line has an end portion shaped as a question mark to orthogonally traverse said slot line.
 6. Apparatus as claimed in claim 1, wherein said conductive plate has an edge portion and said slot line is formed within said conductive plate of said strip line, having opposed surfaces curved away from each other as said surfaces approach said edge portion.
 7. Apparatus as claimed in claim 1, wherein said waveguide has a cross-section of a circular configuration.
 8. Apparatus as claimed in claim 1, wherein said waveguide has a cross-section of a rectangular configuration.
 9. Apparatus as claimed in claim 1, wherein a conductive member is disposed between the periphery of said waveguide and said conductive plate for supporting said strip line within said waveguide.
 10. Apparatus as claimed in claim 9, wherein said support member includes a portion of reduced width disposed upon the periphery of said waveguide. 